Secretory component (SC), ordinarily associated with sIgA in secretions onto mucous surfaces, has been found by immunofluorescence microscopy in human mammary carcinoma cells. This project will attempt to fully define the human tumor-SC system. Various types of tumors will be examined for the presence of SC. Already SC has been found in breast, colon, bronchogenic, renal, and ovarian carcinomas. It seems reasonable to anticipate finding SC in all neoplasms of glandular epithelial origin, both primary and metastatic. Experiments have been done to prove that the SC is actually being produced by the tumor cells and not passively absorbed by them. Sera from patients with tumors will be examined for the presence of free, SC sIgA, and precipitating antibodies to SC. The tumor SC antigenicity will be compared to that of normal SC found in external secretions.